1. Field of the Invention
The present invention relates to a display device having a plurality of displays and a portable electronic device having the display device.
2. Description of the Related Art
Recently, most portable electronic devices comprise a display device having a plurality of displays. For example, a foldable portable terminal formed by pivotally connecting first and second housings via a hinge has a main display on the front surface of the first housing and a sub-display on the rear surface of the first housing. The main display displays all display data such as transmission/reception data, telephone book data, and various control information representing the operating state of the terminal. The sub-display displays control information to be notified of the user in the standby state. The display is generally an LCD (Liquid Crystal Display).
A display device attached to a portable electronic device generally comprises a main display controller and sub-display controller in correspondence with the main display and sub-display. The main display controller and main display, and the sub-display controller and sub-display are respectively connected by independent signal lines. This greatly increases the number of signal lines for connecting displays and display controllers, and the degree of freedom in designing the device decreases.
Especially in a foldable portable terminal, the main display and sub-display are arranged in the first housing, whereas the main display controller and sub-display controller are arranged in the second housing. Many signal lines must be passed through the hinge, which makes downsizing of the hinge and a change in design difficult. Since the number of connector terminals increases in accordance with the number of signal lines, it also becomes difficult to downsize the printed wiring board and housing.
In order to decrease the number of signal lines, there is proposed a technique of transmitting an LCD driving signal from the LCD driver to the LCD panel by time division through a common signal line together with a data signal from an output circuit to a peripheral circuit, as disclosed in, e.g., Jpn. Pat. Appln. KOKAI Publication No. 2000-56733.
According to the conventionally proposed technique, an LCD driving signal to the LCD panel and a data signal to the peripheral circuit are transmitted by time division through a common signal line. This technique does not disclose transmission of display data to a plurality of displays by using a common signal line. Time division transmission requires a time division multiplexing process, resulting in a complicated process and expensive device.